Hydrogenated sugar (also referred to as “sugar alcohol”) means a compound obtained by adding hydrogen to the reductive end group in sugar, and generally has a chemical formula of HOCH2(CHOH)nCH2OH wherein n is an integer of 2 to 5. According to the number of carbon atoms, hydrogenated sugar is classified into tetritol, pentitol, hexitol and heptitol (4, 5, 6 and 7 carbon atoms, respectively). Among them, hexitol having 6 carbon atoms includes sorbitol, mannitol, iditol, galactitol, etc. and in particular, sorbitol and mannitol are very useful materials.
Anhydrosugar alcohol has a diol form with two hydroxyl groups in the molecule, and can be produced by using hexitol derived from starch (for example, Korean Patent No. 10-1079518 and Korean Laid-open Patent Publication No. 10-2012-0066904). Because anhydrosugar alcohol is an environmentally friendly material derived from recyclable natural resources, it has received much interest for a long time and researches on its production continue to proceed. Among such anhydrosugar alcohols, isosorbide produced from sorbitol has the widest industrial applicability at present.
Anhydrosugar alcohol can be used in various fields including treatment of heart and blood vessel diseases, patch adhesive, medicaments such as mouthwash, etc., solvents for compositions in the cosmetics industry, emulsifiers in the food industry, etc. In addition, it can increase the glass transition temperature of polymer materials like polyester, PET, polycarbonate, polyurethane, epoxy resin, etc., and improve the strength of such materials. Furthermore, because anhydrosugar alcohol is an environmentally friendly material derived from natural resources, it is very useful in the plastics industry such as bioplastics and the like. It is also known that anhydrosugar alcohol can be used as an adhesive, environmentally friendly plasticizer, biodegradable polymer, and environmentally friendly solvent for water-soluble lacquer. As such, anhydrosugar alcohol is receiving much interest because of its wide applicability, and the level of practical industrial application thereof is increasing.
Anhydrosugar alcohol after purification and concentration has problems of the lowering of pH and the lowering of UV transmittance, particularly in summer with high temperature.
Korean Patent No. 10-0939431 introduces a technique of adding a reducing agent such as NaBH4 or an antioxidant such as butylated hydroxy toluene (BHT, 2,6-di-t-butyl-4-methylphenol) to distilled anhydrosugar alcohol, in order to improve stability of the anhydrosugar alcohol. However, the storage stability of anhydrosugar alcohol is not improved sufficiently by this method, and thus it is difficult to prevent the lowering of pH and UV transmittance of anhydrosugar alcohol according to long term storage. In addition, additive such as morpholine is not preferable since it smells bad and thus exerts bad influence on workability and product quality.